This invention relates to systems and methods for producing blow-molded plastic articles, and more particularly, for identifying and rejecting defective blow-molded plastic products during the process of making blow-molded plastic products.
Blow molding of containers and other products is a well-known process in which a heated thermoplastic preform is loaded into a mold and filled with pressurized blow air to expand the preform to the shape of the mold interior surface. For example, U.S. Pat. No. 5,683,729, entitled xe2x80x9cApparatus for Making Containers by Blow Moulding Plastic Parisons;xe2x80x9d U.S. Pat. No. 5,863,571, entitled, xe2x80x9cMachine for Making Containers by Blow Moulding Plastic Parisons:xe2x80x9d U.S. Pat. No. 4,427,360, entitled xe2x80x9cApparatus for blow Molding Plastic Articles from a Parison;xe2x80x9d and U.S. Pat. No. 4,943,228, entitled, xe2x80x9cBlow Molding Machine,xe2x80x9d illustrate an injection blow molding process for containers. Each of these patents are incorporated herein by reference in their entireties.
The air pressure within the preform may begin at about 75 pounds per square inch (xe2x80x9cPSIxe2x80x9d) and reach approximately 550 PSI during the active blow stage. The molds typically have small vents near the split lines and/or near the base to permit air to escape from the mold as the preform expands. U.S. Pat. No. 5,792,491, entitled, xe2x80x9cDevice for Sealing a Plastic Container Preform to a Blow Moulding Nozzle,xe2x80x9d which is incorporated herein by reference in its entirety, illustrates a mold for a container.
Even though the preform wall is designed to remain continuous throughout the blowing process to form a continuous container that holds the intended contents, holes or discontinuities in the wall of a finished container sometimes occur that render the container useless. Because such defective products often are not identified during an inspection process, the defective containers frequently may be shipped to a bottler, where the defective container produces leaks, as well as loss of product and production time. The trend toward decreasing weight and wall thickness of containers exacerbates the problem of discontinuities in the preform or container wall.
A system for rejecting a defective discontinuous container from a container production line is provided. The system includes a blow molding carousel, a sound detector system, and a kick mechanism. The blow molding carousel comprises at least two molds such that each one the molds includes an interior surface corresponding to a shape of the container and a nozzle coupled to the carousel and disposed proximate an opening in said mold. Each one of the molds receives pressurized blow air into the mold through the nozzle. The carousel includes a preform-loading point and a container-unloading point, and may also include a container transfer wheel for transferring a plurality of the containers from the carousel at the container-unloading point.
The sound detector system is an disposed proximate the carousel and outputs a reject signal upon sensing a blow air sound level exceeding a predetermined sound level set point (preferably in decibels). The kick mechanism ejects the discontinuous container in response to the reject signal being output from the sound detector. Preferably, the kick mechanism includes a reject arm that strikes the discontinuous container from the container transfer wheel to eject the discontinuous container therefrom. The sound detector system includes a device, which preferably is a proximity switch) for ascertaining a position of the mold from which blow air is escaping (that is, the mold that is creating the sound that exceeds the predetermined sound level set point).
Thus, a preform contiguously expands within the mold interior surface in response to the pressurized blow air to form the container. A failure of a wall of the preform or the container during expansion forms the discontinuous container having a hole through which the blow air flows to form the blow air sound level exceeding the predetermined sound level set point. The predetermined sound level set point is less than a sound level of the pressurized blow air flowing outwardly through the container hole and the mold.
The system may include a delay that sequences the actuation of the reject arm with a signal from said sound detector. The delay may be any suitable delay that achieves such sequencing, such as a time delay approximately equal to the time interval between the container moving from the sound detector to the reject arm or a preset number of pulses from a proximity switch approximately corresponding to the number of containers between the sound detector and the kick mechanism. A controller may control the sequencing, although any logic, including that in a microphone that senses the sound level, may be employed.
According to another aspect of the present invention, the sound detection system for identifying a defective discontinuous container from a container production line is provided that includes a microphone and a control system. The microphone: senses a sound level proximate a container mold and produces a signal that corresponds to the sound level. The sound level may varying according to whether pressurized blow air flows through the discontinuity and a vent in the container mold.
The control system, which is in communication with the microphone, receives the sound level signal and compares the sound level signal to a predetermined sound level set point. The control system outputs a reject signal in response to the sound level signal exceeding the predetermined sound level set point, which is less than a sound level signal corresponding to pressurized blow air flowing through the container mold vent.
The sound detection system may also include a proximity switch for sensing the position of the mold relative to the microphone, wherein the sound level system is activated in response to the proximity switch indicating that the mold is within a predetermined sensing range of the microphone and deactivated in response to the proximity switch indicating that the mold is outside of the predetermined sensing range. Further, the sound detection system may include a controller that compares the sound level signal to the predetermined set point. The controller generates a reject signal in response to the sound level signal exceeding the predetermined set point and delays generating the reject signal according to the predetermined interval.
According to another aspect of the present invention, a method for rejecting a defective discontinuous container from a container production line is provided that comprises the steps of: (a) sensing a sound level proximate a blow molding carousel comprising at least two molds such that each one of the molds includes an interior surface corresponding to a shape of the container and receives pressurized blow air into the mold; (b) generating a sound level signal that corresponds to the sound level; (c) comparing the sound level signal with a predetermined sound level set point; (d) generating a reject signal in response to the sound signal exceeding the predetermined set point; and (e) rejecting the discontinuous container from the production line in response to the reject signal. Thus, a preform contiguously expands within the mold interior surface in response to the pressurized blow air to form the container and a failure of a wall of the preform or the container during expansion forms the discontinuous container having a hole through which the blow air flows to form the blow air sound level exceeding the predetermined sound level set point.
Further, the method may include a deactivating step and an activating step. The activating step includes activating the method in response to the carousel being disposed in a first circumferential position. The deactivating step disables at least one of the sensing step (a), the generating step (b), the comparing step (c), the generating step (d), and the rejecting step (e) in response to the carousel being disposed in a second circumferential position. The deactivating step preferably may include deactivating at least one of the comparing step (d) and the generating step (d) in a controller. The generating step preferably may include delaying outputting the reject signal to sequence the rejecting step (e) with the sensing step (a). The sequencing step may include delaying the outputting of the reject signal, as described above. The generating step (b) may include may employ a controller.